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Although the autonomic nervous sys- tem (ANS) is composed of portions of both the central nervous viscera: L order 10 mg alavert with amex allergy medicine makes me drowsy. Autonomic Nervous © The McGraw−Hill Anatomy cheap 10 mg alavert amex allergy report chicago, Sixth Edition Coordination System Companies, 2001 436 Unit 5 Integration and Coordination FIGURE 13. Autonomic nerves also sacral portions of the spinal cord, with the exception of the area maintain a resting tone in the sense that they maintain a base- between L3 and S1. Autonomic ganglia are located in the head, line firing rate that can be either increased or decreased. Chains of autonomic ganglia also parallel Changes in tonic neural activity produce changes in the intrinsic the spinal cord along each side. A decrease in the excitatory input neurons and the location of the autonomic ganglia help to differ- to the heart, for example, will slow its rate of beat. Cardiac Muscle Like skeletal muscle fibers, cardiac muscle fibers are striated. Damage to an autonomic nerve, in fact, makes its target spread to all cells in the mass that are joined by intercalated muscle more sensitive than normal to stimulating agents. Because all of the cells in the myocardium are physiologi- Van De Graaff: Human V. Autonomic Nervous © The McGraw−Hill Anatomy, Sixth Edition Coordination System Companies, 2001 Chapter 13 Autonomic Nervous System 437 TABLE 13. Origin of electrical activity Spontaneous activity of myogenic fibers Not spontaneously active; neurogenic action potentials Type of stimuli Action potentials Graded depolarizations Response to stretch By contraction; not dependent on action potentials No inherent response Presence of gap junctions Numerous gap junctions join all fibers together Few (if any) gap junctions electrically Type of muscle contraction Slow and sustained Slow and sustained cally joined, the myocardium behaves as a single functional unit, half times their resting length. Unlike skeletal muscles, their ability to contract when the sarcomeres are stretched to the which can produce graded contractions with a strength that de- point where actin and myosin no longer overlap. Single-Unit and Multiunit Smooth Muscles Furthermore, whereas skeletal muscle fibers require stimu- Smooth muscles are often grouped into two functional cate- lation by action potentials through somatic motor neurons before gories: single-unit and multiunit. Single-unit smooth muscles they can contract, cardiac muscle fibers are able to produce ac- have numerous gap junctions (electrical synapses) between adja- tion potentials automatically. Multiunit smooth muscles have few, if any, gap cally independent from stimulation from action potentials. Car- junctions; thus, the individual cells must be stimulated separately diac action potentials normally originate in a specialized group of by autonomic action potentials through motor neurons. However, the rate of similar to the control of skeletal muscles, in which numerous this spontaneous depolarization, and thus the rate of the heart- motor units are activated. Single-unit smooth muscles display pacemaker activity, in which certain cells stimulate others in the mass. Single-unit Smooth Muscles smooth muscles also display intrinsic, or myogenic, electrical ac- Smooth (visceral) muscle tissue is arranged in circular layers tivity and contraction in response to stretch. For example, the around the walls of blood vessels, bronchioles (small air passages stretch induced by an increase in the luminal contents of a small in the lungs), and in the sphincter muscles of the GI tract. How- artery or a section of the GI tract can stimulate myogenic con- ever, both circular and longitudinal smooth muscle layers are traction. Such contraction does not require stimulation by auto- found in the tubular GI tract, the ureters (which transport urine), nomic nerves. By contrast, contraction of multiunit smooth the ductus deferentia (which transport sperm), and the uterine muscles requires nerve stimulation. The alternate contraction of circu- smooth muscles are compared in table 13. Autonomic Innervation of Smooth Muscles Smooth muscle fibers do not contain sarcomeres (which The neural control of skeletal muscles and that of smooth mus- account for striations in skeletal and cardiac muscle). A skeletal muscle fiber has only one junc- muscle fibers do, however, contain a great deal of actin and some tion with a somatic nerve fiber, and the receptors for the myosin, which produces a ratio of thin-to-thick myofilaments of neurotransmitter are localized at the neuromuscular junction about 16:1 (in striated muscles the ratio is 2:1). By contrast, the The long length of myosin myofilaments and the fact that entire surface of smooth muscle fibers contains neurotransmitter they are not organized into sarcomeres helps the smooth muscles function optimally. Smooth muscles must be able to exert ten- sion even when greatly stretched—in the urinary bladder, for ex- ample, the smooth muscle cells may be stretched up to two and a myogenic: Gk, mys, muscle; genesis, origin Van De Graaff: Human V. Autonomic Nervous © The McGraw−Hill Anatomy, Sixth Edition Coordination System Companies, 2001 438 Unit 5 Integration and Coordination Sympathetic ganglion (paravertebral ganglion) Rami FIGURE 13. Neurotransmitter molecules are released along STRUCTURE OF THE AUTONOMIC a stretch of an autonomic nerve fiber that is located some dis- tance from the smooth muscle fibers. The regions of the auto- NERVOUS SYSTEM nomic fiber that release transmitters appear as bulges, or Both the sympathetic and parasympathetic divisions of the auto- varicosities, and the neurotransmitters released from these vari- nomic nervous system consist of preganglionic neurons with cell cosities stimulate a number of smooth muscle fibers.
The Passive Movement of Solutes Tends to Equilibrate Concentrations FIGURE 2 purchase alavert 10mg without prescription allergy treatment in japan. Any solute will tend to uniformly oc- molecules through the lipid bilayer order 10 mg alavert fast delivery allergy medicine linked to alzheimer's. This movement, example, the diffusion of a solute across a plasma membrane is known as diffusion, is due to the spontaneous Brownian driven by the difference in concentration on the two sides of the (random) movement that all molecules experience and that membrane. Initially, random movement from left to right across explains many everyday observations. Sugar diffuses in cof- the membrane is more frequent than movement in the opposite fee, lemon diffuses in tea, and a drop of ink placed in a glass direction because there are more molecules on the left side. The net results in a net movement of solute from left to right across the result of diffusion is the movement of substances according membrane until the concentration of solute is the same on both to their difference in concentrations, from regions of high sides. At this point, equilibrium (no net movement) is reached be- concentration to regions of low concentration. Diffusion is cause solute movement from left to right is balanced by equal an effective way for substances to move short distances. CHAPTER 2 The Plasma Membrane, Membrane Transport, and the Resting Membrane Potential 23 Diffusion across a membrane has no preferential direc- and the difference in concentration between the two sides tion; it can occur from the outside of the cell toward the in- of the membrane is linear (Fig. The higher the differ- side or from the inside of the cell toward the outside. For ence in concentration (C1 C2), the greater the amount of any substance, it is possible to measure the permeability substance crossing the membrane per unit time. Fick’s law for the diffusion of an uncharged solute solutes of physiological importance, such as sugars and across a membrane can be written as: amino acids, the relationship between transport rate and concentration difference follows a curve that reaches a J PA (C1 C2 plateau (Fig. P includes the membrane these hydrophilic substances across the cell membrane is thickness, diffusion coefficient of the solute within the much faster than expected for simple diffusion through a membrane, and solubility of the solute in the membrane. Membrane transport with these characteris- Dissolved gases, such as oxygen and carbon dioxide, have tics is often called carrier-mediated transport because an high permeability coefficients and diffuse across the cell integral membrane protein, the carrier, binds the trans- membrane rapidly. Since diffusion across the plasma ported solute on one side of the membrane and releases it membrane usually implies that the diffusing solute enters at the other side. Although the details of this transport the lipid bilayer to cross it, the solute’s solubility in a lipid mechanism are unknown, it is hypothesized that the bind- solvent (e. Because there are limited numbers of these carri- A substance’s solubility in oil compared with its solu- ers in any cell membrane, increasing the concentration of bility in water is its partition coefficient. Lipophilic sub- the solute initially uses the existing “spare” carriers to trans- stances that mix well with the lipids in the plasma mem- port the solute at a higher rate than by simple diffusion. As brane have high partition coefficients and, as a result, the concentration of the solute increases further and more high permeability coefficients; they tend to cross the solute molecules bind to carriers, the transport system plasma membrane easily. Hydrophilic substances, such as eventually reaches saturation, when all the carriers are in- ions and sugars, do not interact well with the lipid com- volved in translocating molecules of solute. At this point, ponent of the membrane, have low partition coefficients additional increases in solute concentration do not increase and low permeability coefficients, and diffuse across the the rate of solute transport (see Fig. The types of carrier-mediated transport mechanisms For solutes that diffuse across the lipid part of the plasma considered here can transport a solute along its concentra- membrane, the relationship between the rate of movement tion gradient only, as in simple diffusion. Net movement Simple diffusion Carrier-mediated transport 10 10 Vmax 5 5 1 3 1 2 3 Solute concentration (mmol/L) Solute concentration (mmol/L) outside cell outside cell FIGURE 2. Once all are occupied by solute, further increases in extracellular concentration have no ef- fect on the rate of transport. B, Bound solute readily dissociates from the carrier because of plasma membrane. In this example, solute transport into the cell the low intracellular concentration of solute. The release of solute is driven by the high solute concentration outside compared to may allow the carrier to revert to its original conformation (A) to inside. A, Binding of extracellular solute to the carrier, a mem- begin the cycle again. The throcyte GLUT 1 has an affinity for D-glucose that is about transport systems function until the solute concentrations 2,000-fold greater than the affinity for L-glucose. However, equilibrium is attained much tegral membrane protein that contains 12 membrane-span- faster than with simple diffusion.
Subsequently generic alavert 10mg without prescription allergy shots natural, there was extensive media coverage of women dying from cervical cancers that had been “missed” on prior Pap smears because of “laboratory error cheap alavert 10 mg on-line allergy symptoms under chin. This was reinforced by CLIA 88 that required review of all prior negative Pap smears in the 5 years preceeding a new diagnosis of a high-grade squamous intraepithelial lesion (HSIL) or carcinoma. Thus, a frequent scenario leading to a Pap smear claim involved a false-negative smear “discovered” upon review of prior “negatives” in a woman diagnosed with cervical carcinoma. To put the potential magnitude of this problem in perspective, a study by the College of American Pathologists (CAP) of the 5-year “look back” at previous negative Pap smears following the diagnosis of HSIL/carcinoma found that 10% of prior smears were false-nega- tives for squamous intraepithelial lesion (SIL)/carcinoma (1). If atypi- cal squamous cells of undetermined significance (ASC-US) were included, 20% of prior smears were false-negatives. In 1996, the American Cancer Society predicted 15,700 new cases of cervical can- cer and 4700 deaths. Published studies indicated that 60 to 75% of women dying from cervical cancer either never had a Pap smear or had not had one in the 5 years prior to diagnosis (2,3). Therefore, if one assumed that 40% of the predicted new cases of cervical carcinoma had a single Pap smear in the prior 5 years with a 20% false-negative rate, there was a potential for 1256 new claims for failure to diagnose cervical carcinoma on a Pap smear in 1996 alone! Table 1 Pap Smear/Cervical Cytology Claims, Includes Pathology and Lab Experience Pathology Case Incurred % of Total Path/Lab Experience Report Allocated Mature Frequency Year Claims Indemnity ALAE Severity Claims Indemnity ALAE Exposures Claims (per 100 Docs) 1991 & Prior 66 4,219,200 1,395,335 85,069 13 17 18 1992 14 203,000 156,377 25,670 10 3 7 1590 14 0. The difficulty was aggravated by the fact that Pap smears had long been a “loss leader” for large independent laboratories attempt- ing to gain market share and was reimbursed well below cost by many health insurers, Medicare, and Medicaid. Combined with the deterio- rating liability climate, this caused many laboratories to consider no longer accepting Pap smears. At stake was the survival of the Pap smear as an effective, affordable, widely available screening test for cervical cancer, as well as the future of cytology as a diagnostic dis- cipline. An additional concern was the effect managed care might have on Pap smear liability. Would the trend toward mandating lab test referral to large regional laboratories (their lower marginal costs associated with large Pap smear volumes helped to ameliorate poor reimburse- ment) interfere with pathologist–physician communication and follow- up cytologic/histologic correlation? Would the frequent patient change of plans and doctors interfere with appropriate Pap smear follow-up? What would the impact be of shifting the responsibility for collecting Pap smears and the appropriate follow-up of abnormal results from gynecologists to primary care physicians? Would the frequency of the annual screening Pap smear be reduced by the pressures of cost contain- ment and diminish the opportunity to detect lesions “missed” on prior false-negative Pap smears? At TDC, physician consultants and panels of medical experts peri- odically meet to review claims from each medical specialty as part of malpractice risk management and loss prevention. In an attempt to manage the escalating frequency of Pap smear claims, a panel com- posed of cytology experts and gynecologists met in 1996 to discuss liability issues involving cervical cytology. The panels’ written rec- ommendations (4) were distributed to all insured pathologists, gyne- cologists, and primary care physicians and presented at state and national professional society meetings. LIMITING PAP SMEAR LIABILITY: PANEL RECOMMENDATIONS An Annual Pap Smear is Important An ideal screening test is one that is always abnormal in the presence of disease, that is, it has a sensitivity of 100%. False-positive results are Chapter 13 / Pap Smear Litigation 171 acceptable and are detected by subsequent specific (and expensive) testing. False-negatives are undesirable because patients with disease will be missed. As a screening test for cervical cancer detection, the Pap smear is largely responsible for the 70% decline in deaths from cervical cancer that has occurred over the past 50 years (from 30 to 2. Yet, ironically, the Pap smear falls far short of the ideal 100% sensitivity of a screening test. Although there is a wide range in the reported false-negative rate for a single conventional Pap smear, 15–25% is widely accepted (including both sampling and laboratory false-negatives). A 20–30% false-negative rate has been reported for biopsy-proven HSIL/cancer when Pap tests showing at least ASC-US are considered positive (5). Sampling false-negatives (absence of abnormal cells on the smear) are slightly more common than laboratory false-negatives, which are divided about evenly between screening errors made by cytotechnologists and interpretation errors made by pathologists. Every laboratory has false-negatives—including the very best laboratories and those supervised by experts! The low-grade squamous intraepithelial lesion (LSIL) accounts for most false-negative Pap smears, and about half of these lesions regress spontaneously. For those that progress, the evolution is usually slow; however, 20 to 30% of women with LSIL on Pap smear have HSIL on biopsy. Therefore, in 1996, the consequence of a false-negative was best minimized by obtaining a Pap smear annually (i.
The most common location for the pain of a dissecting aortic aneu- rysm is the precordium safe alavert 10 mg allergy medicine name brand. The sudden onset of a tearing pain between the shoulder blades need not be present best 10 mg alavert allergy medicine coupons. The possibility of this diag- nosis should be kept in mind when an acute myocardial infarction is suspected. A normal electrocardiogram and normal enzymes can help differentiate the two. A timely consultation will benefit both the patient and the family phy- sician. The patient or the patient’s guardian has the right to know all of the information that a reasonable person would need to make an intelligent decision. It is the physician’s duty to provide the information in a manner that is under- standable to the recipient. This is best documented by a signed and witnessed informed consent form. It is best for physicians to use forms that have passed legal scrutiny by their state. Informed consent is not only necessary for invasive procedures but also for examination, diagnostic tests, treatment modalities, and pre- scribed medication. The following list contains information that should appear in all informed consent forms. The nature and purpose of the proposed test, examination, or treat- ment. Risks, including possible side effects or complications, as well as benefits. The consequences of doing nothing or of seeking alternatives that are not advised. Although informed consent will not protect a physician from all charges of professional negligence, it is important to address the most common and most serious risks of a procedure. Risks to be noted are infection, bleeding, colon per- foration, peritonitis, and sepsis. What will a family physician do if spasm or obstruction prevents a complete examination? Her family physician’s record documented that over a period of years he had repeatedly advised a routine Pap smear. How- ever, the record did not establish that he had ever explained the reason for a Pap smear or the potential risks of not having one. The patient’s family was able to successfully argue that if she had known that the Chapter 8 / Risk Management 97 purpose of a Pap smear was to detect cervical cancer, then she might have given consent. A surgeon severed a major nerve while performing surgery for squa- mous cell carcinoma. In his defense, the surgeon claimed that the nerve was so matted down in the tumor that it had to be sacrificed for a complete excision. Unfortunately, the surgeon dictated a generic operative note that made no mention of a difficult dissection. There is a rule in risk management that if it is not documented, then it did not happen. The possibility of severing the nerve was not mentioned in the informed consent docu- ment. The incident occurred in a state that requires an objective standard for informed consent. The plaintiff would have had to show that with full disclosure, a reasonable patient would have rejected the procedure. The consequences of rejecting this surgery would have been devastating, far outweighing the consequences of a severed nerve. Other states adhere to a subjective standard meaning that only the decision of the patient in question is considered. It is advisable for physicians to seek the opinion of an attorney in their own state regard- ing objective and subjective standards for informed consent. Jurors rely heavily on the reliability of contemporaneous medical records.